In high performance, military aircraft gas turbine engines, an afterburner or augmenter is disposed downstream of a core engine for providing additional thrust when desired. The augmenter includes an outer casing, a combustion liner and a plurality of circumferentially spaced apart fuel spraybars for injecting additional fuel when desired for augmenting thrust. Since the core gases from the core engine are typically below autoignition temperature, flameholders are typically required in the augmenter to provide stable regions downstream of the fuel spraybars for ensuring effective combustion of the injected fuel without blowout.
Although the augmenter environment is substantially hot due to the combustion process when the augmenter is in operation, the flameholders are typically uncooled and therefore have a limited useful life. Cooled flameholders are known in the art for improving useful life of the flameholders. However, the introduction of a cooling fluid in the hot environment of the augmenter necessarily creates substantial differences in temperature between the relatively cold and hot components of the flameholder. Flameholder designs having integral components subject to large differences in temperature from hot to cold are subject to low cycle fatigue therefrom which again limits the useful life of the flameholder assembly.
In order to initiate augmenter operation, a suitable ignition system therefor is required. Typical augmenter ignition systems are relatively large which undesirably increases weight and complexity. They include a fuel injector and an igniter disposed in a sheltered zone for ensuring stable ignition of the fuel/air mixture within the zone. The components are typically uncooled and therefore are subject to varying differential operating temperatures which effect low cycle fatigue thusly limiting the useful life of the ignition system. Furthermore, the ignition system is typically different in configuration then the radial and/or circumferential flameholders typically used in an augmenter and therefore has a single function of initiating combustion.
As the performance of an augmented aircraft engine increases, the temperature of the core discharge gases which are channeled to the augmenter also increase, and are therefore limited by the ability of the flameholder and ignition system to withstand such increased inlet temperatures without an undesirable useful life. Without suitable cooling of the flameholders and ignition system, a suitable useful life thereof is not attainable for such higher inlet gas temperatures. An improved, cooled flameholder assembly is disclosed and claimed in the application referenced above in the cross reference section which provides cooling for a radial flameholder assembly using relatively cold cooling air, with the different components of the assembly being suitably mounted to allow differential thermal expansion between the components without restraint for reducing low cycle fatigue. A complementary, cooled ignition system is the subject of the present invention.